1. Field of the Invention
The invention relates to a wet frictional material for use in a clutch and a brake in a wet-frictional engagement apparatus.
2. Description of the Prior Art
FIG. 6 shows an example of the configuration of a wet-frictional engagement apparatus. In the drawing, torque is transmitted through contact between driving plates 2 fitted in a spline portion 51 of a hub 5 inserted onto an input shaft 6 and driven plates 1 fitted in a spline portion 41 of a retainer 4. The reference numeral 3 designates a pressure plate and the reference numeral 7 designates a piston for pressing.
Presently, such a frictional engagement apparatus is required so that the apparatus is small in size and light in weight in view of problems of energy, environment, the apparatus is small in operation shock, and the apparatus is high in torque capacity. Further, the frictional engagement apparatus is required to cope with realization of high-energy car engine with realization of high rotational speed and high output thereof. The above-described requirements are extremely strong.
In the conventional frictional engagement apparatus, an additive for reducing the friction coefficient is mixed to lubricating oil to suppress self-induced vibration, for example, vibration of a clutch using slip control to thereby reduce fuel consumption rate. Further, lubricating oil containing an additive for reducing the friction coefficient has been widely used in order to reduce an operation shock, and, therefore, miniaturization of the frictional engagement apparatus inevitably causes low torque capacity. Accordingly, since the operational pressing force is made high to increase the torque capacity, it is necessary to take the safety factor into consideration in order to solve the following problems: resulting in defects relating to reduction of the separation life of a wet frictional material, generation of heat spots and thermal deformation in a mate-frictional surface (driven surface), increase in size of an oil pump, endurance life such as leakage of operational oil. In addition, it is difficult to reduce the size of the apparatus per se.
In the prior art, there has been a problem to be solved in that the frictional material corresponding to the above-described frictional engagement apparatus tends to be thermally disadvantageous if the friction coefficient is made to be high, while, on the other hand, the frictional characteristic will deteriorate to thereby generate self-induced vibration if the high heat resistance is required. It has been difficult to establish compatibility between the high friction coefficient and the high heat resistance.